1. Field of the Invention
This invention relates to a device for measuring the inner or internal pressure of filled cans and, more particularly, to an apparatus for determining whether the filled can inner pressure is satisfactory by measuring the reaction force provided by the filled can when the can barrel is pressed in a direction coincident with the diameter thereof.
2. Description of the Related Art
A prior art apparatus for determining the filled can inner pressure by measuring the reaction force provided by the can barrel (can body) comprises a back-up unit and a measuring unit. The distance between a back-up roll of the back-up unit and a measuring roll of the measuring unit is set at a value which is very slightly smaller than the average value of the barrel of filled cans to be measured. The reaction force imparted to the measuring roll engaging a filled can when the can barrel passes through this gap is measured by a load cell to determine whether the inner pressure is satisfactory. The sectional profile of the can barrel, however, is not really circular, but there is an error of about 0.7 mm at the most between the maximum and minimum diameters. Therefore, with the afore-mentioned distance between the back-up and measuring rolls, some cans may pass through the gap between the two rolls without almost being sandwiched by these rolls. Thus, it is impossible to effect an appropriate determination as to whether or not the can inner pressure is satisfactory.
An apparatus having an aim of solving the above problem is disclosed in Japanese Patent Laid-Open Publication No. 157537/84. The disclosed apparatus comprises, as shown in FIG. 5, a back-up unit A, having a cylindrical and rotatable back-up roll 1, a measuring unit B having a measuring roll 3 having a crown-like outer periphery 2 and rotatably supported by a support rod 4 which is mounted in a bearing 5 such that the load applied to said roll 3 is transmitted to a load cell 6 through the rod 4, said load cell 6 contacting one end of the rod 4 and measuring the amount of the load transmitted to said rod 4 via said roll 3; and a conveyor unit having rope belts 7a to 7d, the belts 7a and 7b being adapted to contact both sides of an upper portion of the barrel of a filled can C1, and the belts 7c and 7d in contact with a lower portion of the can barrel, to guide the can C such that the can barrel C1 proceeds through the gap between the rolls 1 and 3. Reference numeral 8 is a filled can support member for supporting the bottom of proceeding filled cans.
In the apparatus disclosed in FIG. 5, the can body is guided in a state sandwiched between the four rope belts to proceed without rotating, and two sets of a back-up unit and a measuring unit are provided to hold said can between them. Each measuring roll thrusts the same portion of the body of a proceeding filled can with a different amount of thrust other. Then each reaction force of the can barrel is measured by each load cell. Finally, whether the internal pressure is satisfactory is determined by comparing the difference between the two measured values with a standard value.
The apparatus for determining the filled can inner pressure disclosed in the publication described above, however, has two sets of back-up and measuring units for low inner pressure filled cans and a unit for measuring the extent of deformation of the end or lid of high inner pressure filled cans. Therefore, the apparatus is complicated and expensive. Furthermore, the measurement is done twice with respect to the same portion of the body of the filled can, and the two measurement values are processed. Furthermore, separate methods of measurement have to be used for low inner pressure filled cans and high inner pressure filled cans. Thus, the determination becomes complicated.